Knife sharpener



March 30, 1954 A. R. SPEARE KNIFE SHARPENER Filed Dec. 31, l952 Patented Mar. 30, 1954 UNITED STATES PATENT OFFICE 8 Claims.

This invention relates to knife sharpeners of the general type in which a knife blade is held at a predetermined angle against the side of an abrasive wheel and manually reciprocated, causing the wheel to rotate.

The principal object of the invention is to provide an eff cient and reliable knife sharpener which requires a minimum of space for operation, which is adapted for use over a wide range of knife sizes without danger of scoring the back of the knife during sharpening, and which is simple and durable in construction.

Further objects relate to features of construction and will be apparent from a consideration of the following disclosure and the acompanying drawings, wherein:

Fig. 1 is a front elevation, partly in section, of a knife sharpener constructed according to the invention;

Fig. 2 is an isometric view base for the sharpener;

Fig. 3 is a detail, somewhat enlarged, showing a knife blade in operative position against the grinding wheel;

Fig. 4 is a view similar to Fig. l, but showing a modification of the sharpener:

Fig. 5 is a vertical section illustrating a further modification of the sharpener shown in Fig. 1;

Fig. 6 is a side elevation of the modification shown in Fig. 5; and

.Fig. '7 is an elevation with parts shown in section of the modification of Fig. 5 but showing the guide surface in a different position of adjustment.

As illustrated in Figs. 1 and 2, the parts of the sharpener are mounted on a base 8 (Fig. 2) which may be molded or otherwise formed from plastic or similar material, the base being shaped to provide two side supports 9 and I 0, the outer surfaces of which may be in the general form of truncated cones integral with a generally rectangular central well or chamber I 2 which is open at its top to accommodate the grinding wheel. On each side of the well I2 are shelves l3 and M having central horizontally aligned semi-cylindrical depressions l and [6. Provision may be made for fastening the sharpener to a table or other surface, and to this end the well [2 and supports may carry mounting lugs I 3a.

Mounted on the side supports 9 and H! are two caps I! and 18 formed with opposing surfaces I9 and 20 which provide back rests for the knife blade. The lower ends of the adjacent inclined of the supporting surfaces l9 and 20 terminate in lips 2i and 22- which overhang the fiat, parallel faces 23 and- 24 at the lower parts of the supports 9 and II), it being noted that the faces 23 and 24 are vertically aligned with the longitudinal walls of the well l2, as shown in Fig. 1. The lower rims of the caps are rabbeted so as to fit the cooperating rabbeted rims of the supports, and the parts may be cemented or otherwise suitably secured together. Between the faces 23 and 24 and extending into the well i2, is the grinding wheel assembly consisting of grinding disk 25 of suitable abrasive material formed with central dishshaped recesses which receive beveled hubs 26 and 21 of wear-resistant material such as glass, agate, hardened steel or the like. The wheel and hubs are held together by an eyelet or hollow rivet 35: which runs through their centers and is headed over at each end, and a pin 3| extends through the rivet with sufiicient clearance to permit free rotation of the wheel asembly. The ends of the pin 3| are supported in the recesses 15 and I6, and the opposed faces 23 and 24 are cut away to fit over the pin.

It' will be noted that the outer faces of the hubs are juxtaposed to the faces 23 and 24 so that the lips 2| and 22 overhang the outer peripheries of the hubs, as shown in Figs. 1 and 3, and with this construction and arrangement of parts, the cutting edge of a knife cannot be inserted between the hubs and the adjacent faces of the supports. In order to insure proper positioning of a knife K (Fig. 3) so that its cutting edge will be ground to the desired bevel, the angle of inclination of the bevel faces of the hubs 26 and. 21, with respect to the axis of rotation a-a of the grinding disk, is an acute angle amb defined by the line 12-22 intersecting the line a-a at point x; and the angle of inclination of guiding surface l9 (or 20), with respect to the axis or rotation a-a, is also an acute angle aye, but substantially greater than the angle orb, but less than and is defined by the line cc intersecting the line (1-11 at point y, as shown in Fig. 3. By increasing the angle aye with respect to the angle aaxb, the bevel of the cutting edge of knife K may be increased.

With this construction and arrangement of parts the upper left hand face of the knife K has a point contact with the guiding surface l9 and the left hand bevel of the cutting edge of the knife has a corresponding contact with the beveled face of the hub 26, thus minimizing frictional drag and consequent scoring of side of the knife. In order to facilitate insertion of the knife Kat the proper angle and maintain it in proper position during the grinding operation, thereis provided a guard 34 in the form of segment of a hollow sphere having a stiffening rib 35, the opposite ends of which are anchored in recesses 36 (Fig. 2) formed in the upper end walls of well I2.

In operation the sharpener is preferably placed on a flat surface where it may be held by one hand or permanently mounted, but if desired, the sharpener can be attached to a vertical surface. The blade which is to be sharpened is inserted in the space between. one of' the: caps and the grinding wheel and drawn back and forth, causing the wheel 25 to rotate and thus grind the beveled surface of the blade to the desired angle;

after which the knife is withdrawn and inserted in the space between the other cap and opposite face of the grinding wheel and the-operation repeated. It will be observed that. the beveledsurface of the knife has a surface contact with the grinding wheel and the cutting edge remains at all times out-of-contact with the hub so that it is: not, injured. During the operation the -grin'dings drop. down into thev well l2 from which they may be removedfrom time to time.

Although the sharpener illustrated in Figs. 1 and: 2 is quite satisfactoryfor most uses as it produces asmoothly ground cutting edge,v there is a slight frictional drag at the upper edge of the blade which is not ordinarily objectionable on kitchen knives, but nevertheless may be overcome by the arrangement shown in Fig. 4, and is: therefore especially suitable for sharpening highly polished table and carving knives. This embodiment is, in principle, the same as that abovedescribed andthe same or similar reference characters are applied to corresponding parts.

The supports 9a and. Illa. are slightly higherthan those of the first embodiment and each is formed withv an axial sleeve 40- integral with its upper part. Between the sleeve Ml'and its inner surface, each support. is vertically: recessed to permit insertion of the grinding wheelassembly and a plug 42. has a pressed fit in the recess. The upper face of each support is formed: with a shallow circular recess to receive a ball-bearing memberv M concentric with sleeve 40.

Conical caps Ha and Mia. are formed with axial.

depending stems 45' which extend'through' sleeves All sothatthe base of each cap is rotatably supported by a ball bearing member 44, and, the lower end portion of each stem is circumferen tiallygroove-d to receive a snap ring 45 which holds the cap in position. In this embodiment,

as in the previously described embodiment, the peripheral edges or. lips 21a and 22a of the caps overhang the hubs 26 and 21. The operation. is the same as above described except that the guiding surfaces of: the caps have a rolling contact with the upper edge of the knife as it is drawn back and forth, thus eliminating frictional drag and consequent scoring.

Figs. to '7. illustrate another modification of the. invention embodying the same operating principle as previously described, but is designed to give a wide range of adjustability so that the included angle defined. by the ground surfaces may be' varied from a relatively blunt angle, as inv boning knives, to a much smaller angle, as in carving knives, and here again the same or similar reference characters designate corresponding parts. In this embodiment the base is formed with two. supports 91) and Iilb with an intervening well. [2b and. the upper parts of these supports carry bearings for the grinding wheel assembly. At. its. upper outer face-each support is formed with a slot 50 in approximate alignment with a vertical plane passing through the axis of the grinding wheel 25 and the upper part of this slot is offset or stepped to provide a shoulder 52 (Fig. 6). The conical caps Nb and l8b generally conform to those of the embodiment of Figs. 1 to 3, except that the inner face of each cap is formed with a slot 54 (Fig. 7) aligned with a vertical plane passing through its.axis,,and.this. slot communicatesv with a vertical opening; defined by a pair of spaced inwardly directed flanges 55 integral with the cap.

A bell crank 55 fits within each support and associated cap so that one arm 51 projects outwardly through slot 50 and the other arm 58 extends upwardly through slot 54 with its outer edge providing; a knife guide corresponding to the surface I9 (01' 2B) of the embodiment of Figs. 1 to 3-. The bell crank 15, supported for pivotal movement by a pintle 60 which extends through the flanges- 55 and-is held properly: centered by a pair ofv spacers 62 (Fig. 6) cemented or otherwise" secured to the flanges 55. 7

With the construction and arrangement of parts thus described the arm 51 projectingthrough slot- 50- provides a handle by means of which the bell' crank may be swung from the position shown in Fig. 5 to that shown in- Fig. '7, wherein the undersurface of the arm 51 engages and is frictionally held by the shoulder 52; In either position the bend of the-bell crank at the junction of its arms provides a lip 21b which overhangs theadjacent hub of the grinding wheel assembly and thus prevents improper positioning of a knife, as in the previously describedembodiments. Moreover, the angular relationship of the outer edge of arm- 58 and the bevel of" the. associated hub corresponds tothose of the pre vious embodiments.

When the parts are in the position shown in Fig. 5, with arm 51 at the lowermost positionv in slot 58', the outer edge of arm- 58'i's substantially parallel to the adjacent surface of the associated cap, in which position it is set to support a knife- 5 to be ground at a relatively blunt angle; but when the bell crank is swung to the position shown, in Fig. 7 the'arm 58 isset to support a knife to be ground at a relatively small angle. In all other" material particulars the operation isv the same as that described in connection with Figs..1 to.3.

While'I have shown and described different dersirable embodimentsofthe invention, it is to be understood that this disclosure is for the pur-- pose of illustration and that various changes and modifications may be made. without departing. from the spirit and scope of. the invention as set. forth in the appended claims.

I claim:

1. A knife sharpener comprising a. base, an. abrasive. wheel rotatably mounted on saidbase, a. circular hub concentric with said grindingwheelr and juxtaposed to one face thereof,.said hub.having a beveled peripheral surface facing, said. abrasive wheel so as to definetherewith an annu-- lar recess ofV-shaped cross-section, and a back rest mounted on said. base and having aguiding: surface extending downwardly towardv said: abrasive wheel with its lower end overhanging and disposed inwardly of the outer peripheral edge of said hub, the angularity of said beveled peripheral surface withrespect to the axis of rotation of said abrasive wheelbeing such-as to define an acute angleand the slope of said guiding. surface with. respect. tosaid axis of; notation. ta

ing such as to define an angle greater than said acute angle, but less than 90.

2. A knife sharpener as set forth in claim 1, wherein a well adjoins said base and surrounds the lower part of said guiding wheel.

3. A knife sharpener as set forth in claim 1, wherein said back rest is rotatably mounted on said base.

4. A knife sharpener as set forth in claim 1, wherein said back rest is in the form of a cone rotatably mounted on said base about an axis at right angles to the axis of rotation of said abrasive wheel.

5. A knife sharpener as set forth in claim 1, wherein said guiding surface is angularly changeable.

6. A knife sharpener as set forth in claim 1, wherein a second back and a second hub are constructed and arranged with respect to the opposite face of said wheel in the same manner as the first mentioned back rest and hub with respect to said one face of said wheel.

7. A knife sharpener as set forth in claim 1.

6 wherein said guiding surface is defined by one arm of a bell crank pivotally mounted on said base, the other arm of said bell crank providing an adjusting member for varying the angularity of said guiding surface, and means for releasably locking said other arm in adjusted position. 8. A knife sharpener as set forth in claim 1, wherein a guard in the form of a segment of a hollow sphere extends about said abrasive wheel with its central portion projecting laterally beyond the opposite faces of said wheel.

ALBERT R. SPEARE.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 557,051 Cohen Mar. 24, 1896 730,706 Rose June 9, 1903 1,092,877 Wallace Apr. 14, 1914 2,232,402 Norton Feb. 18, 1941 2,496,139 Vars Jan. 31, 1950 

